1. Field of the Invention
The present invention relates to a controller for controlling a printer for printing out images responsive to data sent from a data processor such as a host computer, expecially to a printer controller for controlling an electro-photographic printer such as a laser printer.
2. Description of Related Art
In general, information sent from a data processor is comprised of printing data indicating real image patterns to be printed and control data for controlling the printing method and the mode of a printing engine of the printer. The printer controller processes these data to transform them to dot images to be printed and transmits them to the print engine in order to print out these dot images thereby.
Recently, electro-photographic printers such as laser printers have been widely used because of a high speed of print, an excellent quality of print and quiet printing action.
However, they are still expensive and, therefore, a few data processors share one printer with each other usually. In such case, it becomes necessary to switch respective data processors to the common printer by a suitable switching means such as a multiplexer upon printing.
Since the printer has only one memory for memorizing information related to the print mode such as a number of copies, a size of copy paper, margins and a font of print, the print mode after switching from one user to another may be subjected by the latest print mode before switching. Alternatively, the print mode information before switching is destroyed by designating another print mode when the printing operation is interrupted by another user during an interval thereof.
Conventionally, in order to solve these problems, data of an initial setting file is sent before transmission of print data to initialize the printer wherever the switching is done. However, the initialization of the printer by the initial setting file is very complicated because items to be set become many in a multi-functioned printer. It is also possible by restarting the printer. However, in this case, it can be done only after the completion of the present printing operation and is inconvenient for a remote user since it is difficult to confirm active and inactive states of the printer.
In order to solve the latter problem, it may be considered that a state code indicating the present state of the printer is sent back from the printer to the main host-machine and the main host-machine sends the state code to individual terminals (users). However, the conventional printer is not designed taking into consideration for the common use and, accordingly, it is impossible for the multiplexer or the main host to discriminate the terminal to which the state code is to be sent.